Gorse
The spiny competitor
Back to the Forest Practices Branch
Gorse is a spiny shrub from the Mediterranean region of western Europe. This
shrub has been introduced to other countries where it competes very successfully
with native vegetation. Gorse is suited to mild maritime climates like those of
southwestern B. C. It readily competes for well-drained areas where the soils
have been excessively disturbed or are naturally poor. Gorse has become
increasingly prevalent on roadsides, newly harvested and other disturbed sites in
south coastal areas. There is concern that gorse is spreading and could pose a
greater threat to forests and other resources.
Gorse originates in the Mediterranean
region of western Europe
What is gorse?
Gorse is a dense, spiny, dull greyish-green shrub that typically
grows to about three metres in the Pacific Northwest. It has small leaves that
are generally shorter than its conspicuous spines. From early spring, yellow
pea-like flowers develop in clusters on the ends of its branches becoming hairy
black seed pods by late summer. A typical shrub produces about 8000 seeds
annually. Gorse seed can lay dormant in the soil for up to 40 years and still
germinate. Soil disturbance during road building and tree harvesting present
opportunities for the successful germination of seed.
Gorse typically grows to a height of about three metres in
southwestern B.C.
Like many introduced
plants, gorse is well adapted to survive in a number of environments. The deep
roots and small leaf area allow gorse to establish in dry areas. As gorse
tolerates moderate shading, it can thrive under a partial tree canopy or in the
open. Unlike many plant species, it is able to 'fix' or remove nitrogen from the
air. This adaptation allows it to grow in poor soils.
When established, gorse
produces large amounts of litter. Litter can accumulate and acidify the soil,
excluding plants that do not tolerate acid conditions.
Gorse is also well known for its longevity. In New Zealand, gorse can live up to
30 years, reaching heights up to seven metres. Stump diameters of the older
shrubs range between two and 10 centimetres with occasional older stems greater
than 20 centimetres. It is not uncommon for gorse to become top heavy and topple
when around 12 to 15 years old.
Origin and spread of gorse
Gorse originates in western Europe. It was introduced into New Zealand by
settlers and sold by seed merchants and nurseries for private cultivation until
the 1890s. Since then it has spread to cover more than three per cent of the
total land area in New Zealand, including significant agricultural areas and
forest plantations.
In North America, gorse was first introduced in south coastal Oregon. It has
spread as far south as San Diego County and north through Washington State into
coastal British Columbia. It is thought that it arrived in B.C. 20 to 40 years
ago.
Today, gorse is found in B.C. at lower elevations on sites with mild maritime
climates and seasonal, but not terribly severe, summer droughts. A significant
area along the B.C. coast including Southern Vancouver Island, the Gulf Islands
and the Queen Charlotte Islands, is climatically suited to gorse. There is
concern that further expansion of its range along the coast may be possible.
Is gorse a problem?
With its aggressive colonization and spiny nature, gorse can
make a site virtually inaccessible. It also excudes most native
plants from the sites it inhabits
Gorse is a very aggressive colonizer and appears to be well suited to B.C.
coastal climatic conditions far beyond its present known range. Due to its spiny
nature, it has the potential to make a site virtually inaccessible to everyone.
In its native habitat, there are insects adapted to
diminishing the amount of seed reaching maturity. In B.C., however, there are
no natural enemies to control it.
Gorse contains a high concentration of oil in its branches. As a result it can be
a fire hazard where it is abundant on dry sites. Many areas of coastal B.C. with
gorse thickets are potential sites for wildfires that could cause property
damage.
Gorse may be a fire hazard where it occurs
in dense thickets on dry
sites
This shrub also threatens the biodiversity of areas where it establishes. It
tends to exclude native vegetation by establishing itself quickly with a carpet
of individual plants. Once established, gorse can successfully occupy a site
indefinitely. As it is hardier than many of our native plants and establishes
easily on dry sites and poor soils, gorse has probably not reached the limits of
its range in our province.
How is gorse spread?
Gorse seed can scatter to adjacent areas when its pods burst and eject the
seeds. The seeds can also be spread by animals, water and machinery. It is likely that
seeds are dispersed by vehicles that pick them up in mud and gravel along
roadsides and distribute them along roads adjacent to forest land. Seeds are also
readily transported by water as
Flowers of a typical gorse plant. Gorse can produce about 8000
seeds per year. In its native territory local insects eat the seed,
reducing the threat of gorse spreading. In B.C. there are no
natural
controlling agents
the hard seed coat provides protection from abrading gravels in streambeds.
Gorse can quickly become established on disturbed sites within its range where a lack
of moisture and nutrients limits the rapid establishment of native vegetation. As
gorse has not become well established throughout its potential range in B.C.,
the most effective control is to prevent it from spreading further.
How can the spread of gorse be prevented?
- Early detection and prompt control of gorse in newly infested areas.
- Sites prone to gorse infestation should be planted with preferred vegetation
immediately following disturbance.
- Do not plant gorse. Be aware of its methods of spreading.
- On removal of gorse from a location, plant alternate vegetation immediately,
fertilize and water if necessary to help new vegetation become established. Use
native or less aggressive vegetation adapted to the site conditions.
- Inform others about the danger that gorse poses to the plant diversity of our
forests.
How is existing gorse controlled?
Gorse is not killed by cutting or burning the top growth. Gorse is difficult to
eradicate and, in most instances, requires a combination of treatments to remove
it from a site. Control methods include:
- Burning followed by herbicide treatment of the new sprouts. Gorse burns well,
but tends to resprout from the burned stumps within one month. Treatment with a
herbicide may control the new sprouts. However, after a fire, conditions are
ideal for banked seed to germinate, which may necessitate further herbicide
treatments or grazing.
- Cutting or chopping followed by fire, grazing or herbicides. The gorse is cut
manually or with mechanical implements such as bulldozers. It is then burned to
remove the mature vegetation and to encourage sprouting. The resprouts can be
grazed by goats within three months, or treated with herbicides.
- Cutting followed by seeding. The gorse is cut to ground level and the site is
seeded to a cover crop such as grass. The site is monitored periodically for
gorse sprouts, which are removed.
- Grazing. Although sheep and goats have low preferences for gorse, they have
been used to control it successfully in New Zealand.
- Herbicides. Several herbicides have proven effective in controlling gorse. For
detailed information on chemical control, contact the local Forest Service office
or a certified weed control specialist.
-
Once gorse becomes established it can be very difficult to
control. Gorse is best controlled by not providing it with an
opportunity to become established
What is being done?
The British Columbia Forest Service is:
- Investigating the impact of gorse on crop trees and other non-timber resources.
The investigation includes the extent of its spread into forested areas, and the
fire risk areas where gorse is concentrated.
- Determining effective means to combat gorse in British Columbia. Control
methods used by other jurisdictions are being investigated.
- Tracking the present geographic location and spread of gorse.
- Informing the public about the present locations and control of gorse. If you
know of any areas to which gorse has recently spread, please contact your local
Forest Service office.
Conclusions
- Activities such as road development and timber harvesting can cause soil
disturbance, providing an opportunity for gorse to establish.
- It is important that gorse be recognised as a threat to biodiversity.
- Preventative measures should be taken to limit its spread.
For more information:
Contact the nearest British Columbia Forest Service regional or district office
or write to:
- Forest Practices Branch,
- P.O. Box 9520 Stn. Prov. Gov.
- Victoria, British Columbia,
- V8W 9C2
Contact Tim Ebata tim.ebata@gems8.gov.bc.ca. if you have comments on the presentation of this information.
